Device for shielding a transponder, method for producing a corresponding shielding and transponder provided with said shielding

ABSTRACT

A unit for shielding a transponder includes at least a chip and an antenna structure with application-specific spatial dimensions and which is secured to an electrically conductive surface. The unit includes a film having formed thereon or therein a highly permeable material at least in an area having the spatial dimensions of the antenna structure of the transponder. The highly permeable material is subdivided into elongate shielding elements and free spaces arranged between the respective shielding elements such that when the substrate has been attached to the transponder, the shielding elements will be oriented parallel to a magnetic field induced in the antenna structure of the transponder, so as to suppress eddy currents which are generated by the electrically conductive surface in the antenna structure, when the transponder is being introduced in a magnetic field of a respective reading device.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a shielding for a transpondercomprising at least a chip and an antenna structure.

2. Description of the Related Art

In many spheres of public life, RFID systems for identifying arbitraryobjects have increasingly been used within the last few years. The termRFID stands for Radio-Frequency-Identification and designates anidentification by means of radio waves. An RFID system always comprisestwo components: an evaluation device that can be implemented as a readand/or write unit, and a transponder carrying the data used foridentification.

Transponders which are nowadays produced comprise a small-area chip andan antenna structure. The most common use of transponders arecontactless chip cards, which are nowadays predominantly used as meansof payment in the form of cheque cards, or as access examination meansin the form of access tickets or corporate identification cards, theidentification data in question being stored in a storage means of thechip. Contactless chip cards allow simple handling, they are robust andtheir susceptibility to interference is therefore low, and they offer aplurality of interesting possibilities of use.

Progress in the field of silicon technology allows extremely low-energy,passive transponders. It is, in particular, possible to realizetransponders which are fed with energy from a high-frequency field (HFfield) and which store data by means of this energy and re-transmitthese data by means of a damping modulation. When data are transmittedin this way, the transmission bandwidth is limited to a fraction of acarrier frequency for fundamental electrotechnological reasons, the datarates realized at present being approx. 58 kbits. Further developmentsin the field of chip technology will presumably lead to chips which arecapable of storing a data amount of approx. 1. Mbit on a chip area ofapprox. 1 mm². Reading of such an amount of data will take about 18seconds with the bit rates realized today.

In order to increase these data rates, it will be necessary to usehigher carrier frequencies; this will be possible due to furtherdevelopments in the field of chip technology, especially in the field ofCMOS technology, since circuits having a clock rate of 1 GHz and morecan be realized, not least in view of the continuous reduction in sizeof the structures in question.

The antenna structure of commonly used transponders is implementedeither as a conductor loop or as a dipole. The implementation as aconductor loop allows inductive incoupling of the signal and offers theadvantageous possibility of resonant operation. In order to achievethis, the conductor loop is connected to a capacitance so as to form anoscillating circuit, which is tuned to the operating frequency of thecontactless chip card and which defines together with a coil of theevaluation device a loosely coupled transformer.

Such inductive transponders are capable of exchanging data with anevaluation device over a distance of a few centimetres to a few meters.Transponders used for this purpose are usually operated in a frequencyregion of a few MHz, normally at the allowed frequency of 13.56 MHz. Inview of the fact that the energy required for operating the chip isreceived from the evaluation device via the conductor loop in acontact-free manner so that the transponder need not be provided with avoltage source of its own and will behave absolutely passive especiallyoutside of the operating range of the evaluation device, the necessarynumber of windings of the conductor loop will be too high in the case oflower frequencies and the inductances will be too low in the case ofhigher frequencies for realizing a conductor loop of sufficient quality.

In cases in which the antenna structure is implemented as a dipole, thetransponder can be used in a so-called “close-coupling system” as wellas in a “long-range system”.

Close-coupling systems are RFID systems with a very short range in whichthe dipole of the transponder allows a purely capacitive incoupling ofsignals from an evaluation device, which is located at a small distanceof approx. 0.1 cm to 1 cm from the transponder and which is alsoprovided with suitable electrode surfaces. For coupling in the signal,the two dipoles are placed parallel to one another and define thus platecapacitors via which data and/or energy is/are transmitted.

In the case of long-range systems, ranges of 1 m to 10 m distancebetween the transponder and the evaluation device can be achieved. Inlong-range systems the dipole is implemented as a dipole antenna and itis operated at very high frequencies, said frequencies being approx.2.45 GHz and 5.8 GHz in Europe at present. An evaluation device emitspower which is present at the terminals of the dipole antenna of thetransponder as a HF voltage and which, after having been rectified, isused for feeding the chip.

The production of extremely thin chips, which are connected to conductorloops or dipoles that are thin as well, allows the formation ofextremely thin transponders, so-called Smart or RFID labels. In the caseof many applications of RFID labels it will make sense to operate theselabels on metal surfaces. A typical field of application is theuniversal identification of goods in a shopping basket in a supermarket.In spite of the logistic advantages, the universal identification willonly make sense and will only be justified if all goods are labeled inthis way as far as possible, i.e., also metallic objects such as tinsand primarily also packets containing a metallized foil.

The mounting of a transponder, including, e.g., a high-frequencyconductor loop, directly on a metallic surface is, however, not easilypossible. The alternating magnetic flux through the metal surfaceinduces eddy currents in the conductor loop which counteract the cause,i.e., the field of the conductor loop, and which therefore damp themagnetic field on the surface to such an extent that a supply of energyto and data transmission from the chip of the transponder are no longerpossible.

By inserting highly permeable materials, such as ferrites, between theconductor loop and the metal surface, the formation of eddy currents canbe reduced and largely avoided. A magnetically highly permeable layerbetween the conductor loop and the metal support will conduct the fluxlines closer to the conductor loop according to its magneticconductivity; less flux lines will penetrate into the underlying metaland, consequently, less eddy currents will be induced. This will,however, have the effect that the inductance of the conductor loopchanges and that the oscillating circuit will be detuned so that theresonant frequency will become lower. Fundamentally, the self-inductancewill be increased by ferromagnetic materials and decreased bynon-ferromagnetic materials. The resonant frequency will change in bothcases.

Shielding against high-frequency fields is a general problem that arisesin the field of technology; in the case of RFID technology, this problemhas, however, a special aspect: in RFID systems, the position of theelectric or magnetic field which is to be shielded against or to beconducted more precisely is known because it is defined by the geometryof the antenna structure arranged in close vicinity to the metallicsupport.

For producing the shielding effect, ferrite films are normally used atpresent. These films contain ferrite particles having dimensions in theμm range, which are embedded in polymers and therefore electricallyinsulated from one another. In spite of the high permeability of theindividual particles, an only low overall permeability of typicallyapprox. 10 will be obtained due to the large number of “air gaps”between the particles. A permeability of 10 means that the path lengthof the magnetic flux lines will effectively be reduced by a factor ofapprox. 3; the geometric distance between the RFID label and the metalsupport can be reduced by this factor, with the effect remaining thesame in all other respects.

Higher values can be obtained by compact magnetic conductors, e.g.,layers or compact films of highly permeable metals. For suppressing theabove-mentioned eddy currents, these magnetic conductors must bestructured such that they suppress a flow of current in the direction ofthe induced electric field. Such eddy currents extract energy from thefield, and this will lead, on the one hand, in a reduction of the amountof useful energy that can be transmitted and, on the other hand, in adamping of the antenna circuit with disadvantageous effects on datatransmission. A similar phenomenon is known from the field of electricalengineering, e.g., when mutually insulated blade fins are provided ontransformers.

SUMMARY OF THE INVENTION

Proceeding from the known prior art, it is the object of the presentinvention to provide a possibility of operating an RFID system in metalsurroundings as trouble-free as possible.

This object is achieved by the subject matters of the independentclaims. Preferred embodiments of the present invention are subjectmatters of the subclaims.

The object of the present invention is especially achieved by a unit forshielding a transponder, which comprises at least a chip and an antennastructure with application-specific spatial dimensions and which isattached to an electrically conductive surface.

According to one aspect of the present invention, this unit comprises afilm having formed thereon or therein a highly permeable material atleast in an area having the spatial dimensions of the antenna structureof the transponder. The highly permeable material is subdivided intoelongate shielding elements and free spaces arranged between therespective shielding elements, in such a way that, when the substratehas been secured to the transponder, the shielding elements will beoriented parallel to a magnetic field induced in the antenna structureof the transponder, so as to suppress eddy currents which are generatedby the electrically conductive surface in the antenna structure, whenthe transponder is being introduced in a magnetic field of a respectivereading device.

According to another aspect of the present invention, said unitcomprises a substrate having formed thereon a plurality of fixedferromagnetic particles in an area having at least the spatialdimensions of the antenna structure of the transponder. The respectiveferromagnetic particles are oriented such that, when the substrate hasbeen attached to the transponder, they will be oriented parallel to amagnetic field induced in the antenna structure of the transponder, soas to suppress eddy currents which are generated by the electricallyconductive surface in the antenna structure, when the transponder isbeing introduced in a magnetic field of a respective reading device.

One advantage of the unit according to the present invention is to beseen in the fact that the film or the substrate, which is implemented asa shielding layer, can be comparatively thin. It follows that theshielding layer will be moderate in price and it can be implemented suchthat it can safely be disposed of, i.e., recycled and dumped. Anotheradvantage is that processing is simple: a shielding layer which is thinand which is produced, e.g., in the form of a film can be treated bymeans of paper converting processes. Hence, easy processing into Smartlabels is possible.

The substrate according to the present invention is preferably providedwith ferromagnetic particles on the front and on the back, and it ismade of an electrically non-conductive material, i.e., an organicpolymer. In addition, the substrate can be made of paper.

In particular, the substrate can represent a transponder or an inlay fora transponder.

The antenna structure represents preferably an antenna coil or a closedor an open dipole, e.g., a slot antenna.

The ferromagnetic particles are made, e.g., of iron and belongpreferably to the garnet group of substances (yttrium-aluminumcompounds).

In addition, the object according to the present invention is achievedby a method of producing a shielding for a transponder, which comprisesat least a chip and an antenna structure with application-specificspatial dimensions, the shielding being formed on a substrate. Saidmethod comprises the following steps: applying ferromagnetic particlesto an area of the substrate having at least the spatial dimensions ofthe antenna structure of the transponder; orienting the ferromagneticparticles by means of a constant magnetic field in such a way that, whenthe substrate has been secured to the transponder, the particles will beoriented parallel to a magnetic field induced in the antenna structureof the transponder; and fixing the oriented particles.

The step of orienting the ferromagnetic particles is executed, e.g., bymeans of one or a plurality of permanent magnets, or by means of one ora plurality of electrically excited magnets with a constant magneticfield.

The step of fixing the oriented particles can be executed by means of anadhesive, the ferromagnetic particles being preferably applied togetherwith the adhesive and the fixing taking place during or immediatelyafter the orienting of the ferromagnetic particles.

In addition, the ferromagnetic particles can be contained in a lacquerwhich is applied to the substrate. In this case, the oriented particlesare preferably fixed by thermal drying and hardening of the lacquer.

The ferromagnetic particles are made of, e.g., soft-magnetic iron or ofa ferroelectric material producing a similar effect or of an alloy ormixture producing an effect of the type in question.

The respective ferromagnetic particles preferably have longitudinaldimensions which are comparable with the width of the induced magneticfield, e.g., {fraction (1/20)} to ⅕ of the width of the induced magneticfield.

The ferromagnetic particles are preferably highly permeable and elongatein shape and they each have a length of approx. 300 μm, a width ofapprox. 50 μm and a thickness of approx. 10 μm.

The substrate according to the present invention can be applied to thetransponder after the fixing of the ferromagnetic particles.Furthermore, the transponder can be formed prior to producing theshielding on the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated into and form a part of thespecification for the purpose of explaining the principles of theinvention. The drawings are not to be construed as limiting theinvention to only the illustrated and described examples of how theinvention can be made and used. Further features and advantages willbecome apparent from the following, and more particular description ofthe invention as illustrated in the accompanying drawings, showing:

FIG. 1 a unit for shielding a transponder according to a first aspect ofthe present invention;

FIG. 2 a schematic view of the steps to be executed in a method ofproducing a shielding for a transponder according to the first aspect ofthe present invention;

FIG. 3 a unit for shielding a transponder according to a second aspectof the present invention; and

FIG. 4 a unit for shielding a transponder according to a third aspect ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The illustrative embodiments of the present invention will be describedwith reference to the figure drawings, wherein like elements andstructures are indicated with like reference numbers.

FIG. 1 shows a unit 1 for shielding a transponder, which comprises atleast a chip and an antenna structure 4 with application-specificspatial dimensions and which is secured to an electrically conductivesurface, according to a first aspect of the present invention. Theantenna structure 4 shown in FIG. 1 represents a conductor loop and anantenna coil, respectively.

The unit 1 comprises a substrate 2 having formed thereon a plurality offixed ferromagnetic particles 3 in an area having at least the spatialdimensions of the antenna structure 4 of the transponder.

The antenna structure 4 of the transponder is shown in FIG. 1 only forclearly indicating this area on the substrate 2, said antenna structure4 being, however, not visible when the shielding itself is beingproduced in cases in which the transponder is not formed on thesubstrate 2.

The respective ferromagnetic particles 3 are oriented such that, whenthe substrate 2 has been secured to the transponder, they will beoriented parallel to a magnetic field induced in the antenna structure 4of the transponder, so as to suppress eddy currents which are generatedby the electrically conductive surface in the antenna structure 4, whenthe transponder is being introduced in a magnetic field of a respectivereading device.

The substrate 2 is preferably provided with ferromagnetic particles 3 onthe front and on the back and can be made of an electricallynon-conductive material, e.g., an organic polymer. In particular, thesubstrate 2 can be made of paper. Furthermore, the substrate 2 canrepresent a transponder or an inlay for a transponder. The advantage ofapplying the ferromagnetic material to the front and to the back is tobe seen in the fact that a closed surface is obtained (in a projectionat right angles to the main surface) and that eddy current losses willin this way be suppressed completely.

The ferromagnetic particles 3 are made, e.g., of iron or of an alloyproducing a similar effect or they preferably belong to the garnet groupof substances (yttrium-aluminum compounds) for higher frequencies.

FIG. 2 shows a schematic view of the steps to be executed in a method ofproducing a shielding for a transponder which comprises at least a chipand an antenna structure with application-specific spatial dimensions,the shielding being formed on the substrate, according to a first aspectof the present invention.

In a first step, ferromagnetic particles 3 are applied to a substratearea having at least the spatial dimensions of the antenna structure ofthe transponder. The particles are preferably applied by means of alacquer 5 having a suitable viscosity and containing suspendedferromagnetic particles 3.

The ferromagnetic particles 3 are made of, e.g., a soft-magnetic iron orof a ferroelectric material producing a similar effect or of an alloy ormixture producing an effect of the type in question. The respectiveferromagnetic particles 3 preferably have longitudinal dimensions whichare comparable with the width of the induced magnetic field, e.g.,{fraction (1/20)} to ⅕ of the width of the induced magnetic field.Preferably, the ferromagnetic particles 3 are highly permeable andimplemented as elongate particles, each having a length of approx. 50 to500, preferably 300 μm, a width of 10 to 60 μm and a thickness of 10 to60 μm.

In a further step, the ferromagnetic particles 3 are oriented by meansof a constant magnetic field in such a way that, when the substrate 2has been secured to the transponder, the particles 3 will be orientedparallel to a magnetic field induced in the antenna structure of thetransponder. The ferromagnetic particles are oriented, e.g., by means ofone or a plurality of permanent magnets 6 or by means of one or aplurality of electrically excited magnets with a constant magneticfield. In particular, the particles 3 are oriented in accordance withthe geometry of the antenna structure by the constant magnetic field insuch a way that the particles will be oriented according to theenergy-minimizing principle in the direction of field.

The orienting can also be executed when the substrate 2 has beenattached to the transponder. In addition, the lacquer 5 for producingthe shielding for the transponder can be applied directly to thetransponder so that the formation of an additional substrate 2 as asupport for the shielding can be dispensed with.

In a further step, the oriented particles 3 are fixed to the substrate2. The fixing of the oriented particles 3 can be accomplished by meansof an adhesive, the ferromagnetic particles 3 being preferably appliedtogether with the adhesive and the fixing taking place during orimmediately after the orienting of the ferromagnetic particles 3.

In the event that the ferromagnetic particles 3 are contained in alacquer 5 which has been applied to the substrate 2, the fixing of theoriented particles 3 is preferably accomplished by means of thermaldrying and hardening of the lacquer.

The ferromagnetic particles 3 can also be applied in that they arescattered on the substrate, then oriented and finally fixed.

Another possibility is to combine the steps of applying and orienting inthat the ferromagnetic particles are already punched out in the correctorientation and in that this punched pattern is then applied unchangedto the substrate.

Finally, it is also possible to generate oriented patterns offerromagnetic particles by means of etching techniques, making use of,e.g., photolithographic methods.

The shielding layer produced in this way can then be incorporated in thetransponder structure. The magnetic shielding layer can perhaps beplaced directly on metal, in the event that the magnetic conductor isessentially electrically insulating. Otherwise, attention should be paidto the fact that the shielding layer has to be applied to an electricinsulating layer. According to a preferred embodiment, the shieldinglayer is laminated in, when the transponder is being produced.

According to a specially preferred aspect of the present invention, ashielding or shielding layer is produced on the front and on the back ofthe same thin substrate 2. The application of the ferromagneticparticles 3 is then executed sequentially, i.e., in a first step on thefront and in a second step on the back. In particular, the shieldinglayer applied in the second step is additionally oriented according tothe already existing first oriented shielding layer and is preferablyoriented such that gaps existing in the first layer will be covered.This can be supported, e.g., by a slightly oblique position of theorienting constant magnetic field.

FIG. 3 shows a unit 7 for shielding a transponder, which comprises atleast a chip and an antenna structure 10 with application-specificspatial dimensions and which is attached to an electrically conductivesurface, according to a second aspect of the present invention. Theantenna structure 10 shown in FIG. 2 represents a conductor loop and anantenna coil, respectively.

The unit 7 comprises a film 8 having formed thereon or therein a highlypermeable material in an area having the spatial dimensions of theantenna structure 10 of the transponder.

The antenna structure 10 of the transponder is shown in FIG. 1 only forclearly indicating this area on the film 8, said antenna structure 10being, however, not visible when the shielding itself is being producedin cases in which the transponder is not formed on the film 8.

The highly permeable material is subdivided into elongate shieldingelements 9 and free spaces arranged between the respective shieldingelements 9, in such a way that, when the substrate has been secured tothe transponder, the shielding elements 9 are oriented parallel to amagnetic field induced in the antenna structure 10 of the transponder,so as to suppress eddy currents which are generated by the electricallyconductive surface in the antenna structure 10, when the transponder isbeing introduced in a magnetic field of a respective reading device.

FIG. 4 shows units 11, 12 for shielding a transponder, which comprisesat least a chip and an antenna structure 13, 14 withapplication-specific spatial dimensions and which is secured to anelectrically conductive surface, according to a third aspect of thepresent invention.

The antenna structure 13, 14 represents a dipole antenna, which is hereshown as an open dipole. For reasons of impedance and interferenceimmunity, a so-called slot antenna may, however, be used as well, i.e.,a closed or open dipole are alternatively used, which form, e.g., aso-called slot antenna.

Since the direction of a field to be shielded against is also known inthis case and predetermined by the dipole antenna 13, 14, respectiveferromagnetic particles or shielding elements 15, 16 can here once morebe oriented in a suitable manner, i.e., at right angles to theorientation of the dipole and at right angles to the direction ofarrival.

For reasons of characteristic impedance adaptation and antenna gain,slot antennas 14 are preferably used in the GHz region. Also theseantennas can be shielded with regard to their magnetic field components.Geometrically, the pattern of the structured shielding is here similarto a large-area, open dipole.

The materials used for shielding in the upper MHz and GHz regions arepreferably the substances known from the field of military “stealthtechnology”, which are based on aluminum-iron garnets and analogousalloys.

While the invention has been described with respect to the physicalembodiments constructed in accordance therewith, it will be apparent tothose skilled in the art that various modifications, variations andimprovements of the present invention may be made in the light of theabove teachings and within in the purview of the appended claims withoutdeparting from the spirit and intended scope of the invention. Inaddition, those areas in which it is believed that those of ordinaryskill in the art of familiar have not been described herein in order notto unnecessarily obscure the invention described herein. Accordingly, itis to be understood that the invention is not to be limited by thespecific illustrative embodiments, but only by the scope of the appendedclaims.

1-30. (canceled)
 31. A method of producing a shielding for atransponder, which comprises at least a chip and an antenna structurewith application-specific spatial dimensions, the shielding being formedon a substrate, said method comprising: applying ferromagnetic particlesto an area of the substrate having at least the spatial dimensions ofthe antenna structure of the transponder; orienting the ferromagneticparticles by a constant magnetic field in such a way that, when thesubstrate has been attached to the transponder, the particles will beoriented parallel to a magnetic field induced in the antenna structureof the transponder; and fixing the oriented particles.
 32. The methodaccording to claim 31, wherein the ferromagnetic particles are orientedby one or a plurality of permanent magnets.
 33. The method according toclaim 31, wherein the ferromagnetic particles are oriented by one or aplurality of electrically excited magnets with a constant magneticfield.
 34. The method according to claim 31, wherein the orientedparticles are fixed by an adhesive.
 35. The method according to claim34, wherein the ferromagnetic particles are applied together with theadhesive and the fixing takes place during or immediately after theorienting of the ferromagnetic particles.
 36. The method according toclaim 31, wherein the ferromagnetic particles are contained in a lacquerwhich is applied to the substrate.
 37. The method according to claim 36,wherein the oriented particles are fixed by thermal drying and hardeningof the lacquer.
 38. The method according to claim 31, wherein theferromagnetic particles are highly permeable and elongate in shape. 39.The method according to claim 38, wherein the ferromagnetic particleseach have a length of about 300 μm, a width of about 50 μm, and athickness of about 10 μm.
 40. The method according to claim 31, whereinthe ferromagnetic particles are made of soft-magnetic iron or of aferroelectric material producing a similar effect or of an alloy ormixture producing an effect of the type in question.
 41. The methodaccording to claim 31, wherein the respective ferromagnetic particleshave a longitudinal dimension which is comparable with the width of theinduced magnetic field.
 42. The method according to claim 41, whereinthe said longitudinal dimension of the ferromagnetic particles amountsto {fraction (1/20)} to ⅕ of the width of the induced magnetic field.43. The method according to claim 31, wherein the substrate is appliedto the transponder after the fixing of the ferromagnetic particles. 44.The method according to claim 31, wherein the transponder is formedprior to producing the shielding on the substrate.
 45. The methodaccording to claim 31, wherein the ferromagnetic particles are appliedby a printing technique.
 46. The method according to claim 31, whereinthe shielding layer and the antenna are combined by folding orlaminating.
 47. A unit for shielding a transponder, which comprises atleast a chip and an antenna structure with application-specific spatialdimensions and which is attached to an electrically conductive surface,said unit comprising: a substrate having formed thereon a plurality offixed ferromagnetic particles in an area having at least the spatialdimensions of the antenna structure of the transponder; wherein therespective ferromagnetic particles are oriented such that when thesubstrate has been attached to the transponder, the ferromagneticparticles will be oriented parallel to a magnetic field induced in theantenna structure of the transponder so as to suppress eddy currentswhich are generated by the electrically conductive surface in theantenna structure when the transponder is being introduced in a magneticfield of a respective reading device.
 48. The unit according to claim47, wherein the substrate is provided with ferromagnetic particles onthe front and on the back.
 49. The unit according to claim 47, wherein aplurality of ferromagnetic layers are provided one on top of the other,said layers being, however, separated by insulators.
 50. The unitaccording to claim 47, wherein the substrate is made of an electricallynon-conductive material.
 51. The unit according to claim 50, wherein thesubstrate is made of an organic polymer.
 52. The unit according to claim47, wherein the substrate is made of paper.
 53. The unit according toclaim 51, wherein the substrate represents a transponder or an inlay fora transponder.
 54. The unit according to claim 47, wherein the antennastructure represents an antenna coil.
 55. The unit according to claim47, wherein the antenna structure represents a closed or an open dipole.56. The unit according to claim 55, wherein the antenna structurerepresents a slot antenna.
 57. The unit according to claim 47, whereinthe ferromagnetic particles are made of iron.
 58. The unit according toclaim 47, wherein the ferromagnetic particles belong to the garnet groupof substances (yttrium-aluminium compounds).
 59. A transponder whichcomprises at least a chip and an antenna structure and which is attachedto an electrically conductive surface, wherein at least one unitaccording to claim 47 is provided between the transponder and theelectrically conductive surface.
 60. A unit for shielding a transponder,which comprises at least a chip and an antenna structure withapplication-specific spatial dimensions and which is attached to anelectrically conductive surface, said unit comprising: a film havingformed thereon or therein a highly permeable material at least in anarea having the spatial dimensions of the antenna structure of thetransponder; wherein the highly permeable material is subdivided intoelongate shielding elements and free spaces arranged between therespective shielding elements such that when the substrate has beenattached to the transponder, the shielding elements will be orientedparallel to a magnetic field induced in the antenna structure of thetransponder so as to suppress eddy currents which are generated by theelectrically conductive surface in the antenna structure when thetransponder is being introduced in a magnetic field of a respectivereading device.